It has recently been reported that alphaB-crystallin, a low-molecular-weigh
t heat shock protein, may be released from cells by mechanical stretch. We
investigated a physiological role of alphaB-crystallin in platelet function
. alphaB-crystallin inhibited platelet aggregation induced by thrombin or b
otrocetin in hamsters and humans. These platelets had specific binding site
s for alphaB-crystallin. Moreover, alphaB-crystallin significantly reduced
thrombin-induced Ca2+ influx and phosphoinositide hydrolysis by phospholipa
se C in human platelets. Additionally, plasma levels of alphaB-crystallin w
ere markedly elevated in cardiomyopathic hamsters. Levels of alphaB-crystal
lin in vessel walls after endothelial injury were markedly reduced. Therefo
re, our results suggest that alphaB-crystallin, which is discharged from ve
ssel walls in response to endothelial injury, acts intercellularly as a reg
ulator of platelet function.